The increasing complexity of modern electronic design has led to digital systems with domains that operate at different supply voltages. This leads to digital signals in one domain having a voltage range that is different from the voltage range in another domain. It is not unusual that one domain operating at a low supply voltage must communicate with another operating at a high supply voltage. Consider a microcontroller in data communication with external memory. The core of the microcontroller is powered by a low supply voltage VDDL, while the external memory is powered by a high supply voltage VDDH. The core uses low-voltage digital signals, which switch between VDDL and ground. The external memory expects to receive high-voltage digital signals, which switch between VDDH and ground. The low-voltage digital signals cannot be correctly sampled and stored in the external memory unless they are first converted (i.e., shifted) to high-voltage digital signals. Voltage level shifters can perform this conversion.
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